Diphosphates are known as flameproofing additives. JP 59 202 240 describes the preparation of such a product from phosphorus oxychloride, diphenols like hydroquinone or bisphenol A, and monophenols like phenol or cresol. These diphosphates may be used in polyamide or polycarbonate as flameproofing agents. However, the patent contains no indication of an improved stress cracking resistance due to the addition of the oligomeric phosphate to polycarbonate molding compositions.
EP-A 363 608 describes flame-resistant polymer mixtures of aromatic polycarbonate, styrene-containing copolymer or graft copolymer, and oligomeric phosphates as flameproofing agents. It is mentioned in general that tetrafluoroethylene polymers may be added.
EP-A 0 767 204 describes flame-resistant polyphenylene oxide (PPO) or poly-carbonate mixtures that contain a mixture of oligophosphates (bisphenol A (BPA) oligophosphate type) and monophosphates as flameproofing agents. High contents of flameproofing agents lead to disadvantageous mechanical properties (notched impact strength, stress cracking behavior) and a reduced dimensional stability under heat.
EP-A 0 611 798 and WO 96/27600 describe molding compounds containing polycarbonate and also oligomeric, terminally alkylated phosphoric acid esters of the BPA type. Because of the alkylation, the attainment of effective, flameproofing requires high proportions, which is very disadvantageous for many application engineering properties (mechanics, dimensional stability under heat).
EP-A 0 754 531 describes reinforced PC/ABS molding compounds suitable for precision parts. The flameproofing agents used are oligophosphates of the BPA type, inter alia. The high proportions of filler have a very disadvantageous effect on mechanical properties such as elongation at break or notched impact strength.
EP-A 771 851 describes molding compounds containing aromatic polycarbonate, graft polymer based on diene rubber, SAN copolymer, a phosphate and tetrafluoroethylene polymers, the polycarbonate having various molecular weights. Stability to loss of impact strength, heat stability and moisture resistance are disclosed as advantages.
To achieve an adequate level of flameproofing, the above-mentioned polymer mixtures usually require the presence of small proportions of PTFE as an antidripping agent. In the event of a fire, this prevents the polymer mixture from tending to produce burning drips and igniting materials situated underneath. In certain fire tests, e.g. the UL 94 V test, the avoidance of burning drips after ignition is assessed as particularly favorable and is stipulated as essential for achieving the best assessment, V-0.
U.S. Pat. No. 5,804,654 describes PTFE powders which are partially encapsulated with a styrene-containing polymer or copolymer and which are very suitable as additives V in polyester blends such as PC/ABS. U.S. Pat. No. 6,040,300 describes processes for the preparation of such special PTFE-containing powders.
The object of the present invention is to provide flameproof PC molding compositions modified with a graft polymer which are distinguished by very good mechanical properties, a high degree of fire resistance and a very good stress cracking behavior. In particular, these advantages are also observed at elevated processing temperatures. These molding compositions are thus particularly suitable for applications where contact with special media, e.g. solvent, lubricant, cleaning agent, etc., may occur.